This invention relates to a method for elastifying and extending polymers with EVA copolymers, PVC or PVC copolymers in gel form and to the use of thusly produced compositions.
Molding and joint sealing materials based on mixtures of acrylate copolymer dispersions with fillers, pigments and plasticizers have only minimal elastic properties, and the tackiness of the molding materials produced from these mixtures increases with increasing plasticizer fraction. Such molding and joint sealing materials are useful only for a total deformation of about 10%, so that they are unsuitable for sealing a large number of joints in building construction despite their advantageous price.
Furthermore, moisture-curing one-component molding and sealing materials based on MS polymers (from Kaneka) are known. These sealing materials contain as prepolymers the aforementioned MS polymers which are crosslinkable by atmospheric humidity and which are compounds having silyl end groups with at least one hydrolyzable substituent on the silicon atom. Such prepolymers and molding and sealing materials produced therefrom are known from DE-A-40 19 074 and DE-A-38 16 808. The latter specification describes molding and sealing materials produced from these MS polymers at length with reference to further publications. The disclosure content of the two aforementioned specifications is hereby incorporated in full by reference.
Molding and sealing materials based on MS polymers react with moisture from the air to form elastomers, the surface of which is very frequently highly tacky. Therefore, the use of such materials is not possible wherever soiling with dust takes place or is likely.
It is an object of the present invention to reduce this surface tackiness of molding and sealing materials to such an extent that in the event of contact with dusts of various kinds permanent soiling can be ruled out.
The invention provides the achievement of this object which is discernible in the claims. It consists essentially in adding to the aforementioned molding and sealing materials a gel based on an ethylene-vinyl acetate copolymer (EVA), a polyvinyl chloride homopolymer (PVC) or a vinyl chloride/vinyl acetate copolymer (PVC copolymer and a lasticizer and wax.
The use of vinyl acetate homo- and/or copolymers in adhesives and sealants is known per se. For instance, JP 07197010 A/95 describes a two-component sealant composition consisting of an isocyanate component and a low molecular weight hydroxyl-functional acrylate copolymer which contains vinyl acetate as comonomer. This sealant has low surface tackiness. The use of an ethylene-vinyl acetate gel is not disclosed.
JP-A-87/64881 describes a nontacky contact adhesive containing a thermoplastic resin and a plasticizer; the thermoplastic resin may be an ethylene-vinyl acetate copolymer.
EP-A-295 727 describes latices of interpolymers of vinyl acetate, ethylene and a vinyl ester of a tertiary aliphatic carboxylic acid in which the carboxylic acid component contains 9 carbon atoms. These films are notable for low tackiness.
A method for elastifying and extending polymer compositions selected from the group consisting of acrylate copolymer dispersions, reactive polyurethane polymers, MS polymers, polysulfides and silicone rubbers through the addition of EVA gels is not mentioned in any of the aforementioned documents.
The method of the invention is carried out by initially fabricating a gel from EVA, PVC or PVC copolymer, plasticizer and wax and also, optionally, benzoyl chloride or TI additive (from Bayer). The total amount of the plasticizer needed is initially charged to a stirred tank, and then EVA, PVC or PVC copolymer and wax are added with stirring. This mixture is then heated with stirring to about 125xc2x0 C. and stirred until a clear homogeneous solution is obtained. Stirring is then continued at this temperature for 30 minutes. Subsequently, if desired, 0.1% by weight of benzoyl chloride or TI additive are added. For intermediate storage, this gel is filled into a vessel to be sealed airtight and the intermediate product is then cooled down to room temperature.
In a second operation, the thusly fabricated gel is mixed with the other constituents of the molding or sealing material in a planetary dissolver until homogeneous. These constituents of the molding and sealing materials customarily comprise polymer compositions selected from the group of MS polymers (from Kaneka) or acrylate copolymer dispersions. However, polyurethane polymers, polysulfide polymers or silicone rubbers can be used as well. Suitable MS polymers are described in DE-A-40 19 074 and DE-A-38 16 808 with reference to further publications. The disclosure content of the two last-mentioned documents is hereby incorporated in full by reference.
The molding and sealing materials further contain inorganic fillers such as carbon black, calcium carbonate and pigments such as titanium dioxide and the like and also plasticizers, especially phthalic esters such as diisononyl phthalate or alkylsulfonic acid esters of phenol such as MESAMOLL (from Bayer) or phosphoric esters such as tricresyl phosphate. The materials may finally include customary UV stabilizers and aging inhibitors and also organofunctional silanes, for example 3-glycidyloxypropyl- or 3-aminopropyl-trimethoxysilane or vinyltrimethoxysilane, especially to improve the adhesion to glass, metals, etc.
Particularly the moisture-reactive one-component materials further contain organometallic tin compounds to accelerate the curing, and also moisture scavengers such as carbonyl chlorides, for example benzoyl chloride or TI additive (from Bayer).
The molding and sealing materials based on MS polymers and incorporating the gels of the invention surprisingly exhibit an appreciable reduction in surface tackiness, and this tackiness decreases with increasing EVA copolymer, PVC or PVC copolymer content, despite the associated high plasticizer content. Additionally, an appreciable economic advantage is obtained, since up to about 45% of the original MS polymer fraction can be replaced with the less costly gel.
As mentioned at the beginning, mixtures of acrylate copolymer dispersions with fillers, pigments and plasticizers have only minimal elastic properties, and the tackiness of molding materials produced from these mixtures increases with increasing plasticizer fraction. By adding the inventive EVA, PVC or PVC copolymer gels, optionally in combination with emulsifiers, it is possible to produce elastic molding materials which achieve a total deformation of 25%. Compared with the otherwise customary total deformation of about 10% for acrylate dispersion molding materials, this is an unexpectedly great improvement. Compared with the customary elastic molding materials based on polysulfides, modified silicone rubber, polyurethanes and silicone rubber, such molding materials based on acrylate copolymer dispersions with EVA, PVC or PVC copolymer gels are significantly more economical, given that the other properties such as modulus of elasticity, total deformation and aging resistance are comparable.
The invention is more particularly described by the nonlimiting examples hereinbelow.